How to Mix Saltwater and Perform a Water Change by Scott Brang, MarineDepot.com Reef Squad
Today’s aquarist takes every precaution to keep their aquarium healthy and looking great.
After all, this hobby is a large investment in time, money and effort. One of the greatest factors, often overlooked, is water.
Clean, pure saltwater is the basis for everything in your aquarium. Whether you are battling hair algae or have experienced a string of mortalities, the problem can often be traced back to the water you are putting into the tank. Not only is it important to look at the quality of water used, but also the quantity and frequency of water changes as well.
Our tap water supply contains many different chemicals to make the water safe for human consumption. These same chemicals can, however, be deadly to your tank.
The worst of these toxins are chlorine and chloramines. These additives kill bacteria and other organisms in tap water, but even in low concentrations, will burn the gills of your fish.
It is therefore necessary to pre-treat water before it goes into our tanks.
For a fish-only system, a water conditioner will adequately neutralize chlorine.
For reef tanks, there are other chemicals in tap water that can harm invertebrates, like copper and heavy metals. For these systems, reverse osmosis (RO) filtration is strongly recommended.
Correctly mixing saltwater for a marine or reef aquarium is a vitally important—yet relatively easy—task.
First, find a container that can hold (at least) 5 to 10 percent of the volume of water used to fill your “display” tank. Old aquariums and clean garbage cans are popular among hobbyists, but you can choose whatever works best for your own “mixing tank.”
Next, fill the container with dechlorinated or reverse osmosis (RO) freshwater. It’s a good idea to aerate RO water for 12-24 hours before mixing in the salt. This will drive off excess CO2 which ensures a proper pH and buffering capacity in the synthetic seawater.
Add synthetic salt, being careful to follow the manufacturer’s instructions so you can match the salinity of your mixing tank water to your aquarium water. Ideally, salinity should be 27 to 35 parts per thousand (ppt), or 1.020 to 1.026 specific gravity. Use a refractometer to measure salinity and adjust your level accordingly.
Freshly prepared synthetic seawater is very caustic (capable of burning or corroding), so it will need some time to “cure” before it can be used in your aquarium.
Allow the newly mixed seawater to sit in your container for a minimum of 24 hours before use. During that time, place an airstone or powerhead in the water to circulate and aerate the mixture. Lastly, drop in a heater to match the water temperature to that of your display tank.
The Water Change
There continues to be much debate regarding how much water to change and how frequently to change it.
I have tried every scenario and have learned through experience that a small-to-moderate water change every 1-2 weeks works best.
I know several people who prefer to change 25-30% of the water once each month. By the end of the third week, however, this maintenance routine begins to show its shortcomings.
I prefer a water change of 5-10% of the total tank volume (including sump) every 1-2 weeks. This schedule doesn’t allow nitrates to build up or trace elements to deplete too far.
To begin the water change, turn off your lighting to reduce the stress level in the tank. You may have to turn off some pumps as well, so they don’t run dry.
Be sure to have the replacement water ready at least 24 hours in advance. The temperature and salinity of the replacement water should match what is currently in your display tank.
While siphoning out water, use a gravel vacuum to remove as much debris from the tank as possible. Don’t worry if some of your corals are exposed to air for a short time; in the wild, corals are often exposed to air during low tide.
Once the desired amount of water has been removed, begin adding in the new water. Alternatively, you may opt to have a powerhead replace the water as you siphon to limit the likelihood your corals come into contact with air.
The Importance of keeping saltwater on hand
Saltwater is an invaluable asset for marine and reef aquariums and is often over looked.
A hobbyist can spend countless hours and thousands of dollars (depending on how big the tank is) just to lose it all because he wasn’t prepared. That is why I’m a firm believer in keeping extra saltwater made at all times. In my years as an aquarist, in both public and private settings, I’ve seen countless scenarios where a reserve saltwater tank saved the day. From a tank full of octopus ink that needs an emergency water change to a complete tank failure that left $10K in corals high and dry, a backup saltwater tank is well worth the small cost and effort.
All it really takes is a container that holds at least 10% of your aquarium’s volume, a powerhead and a heater. Personally, I have two 55-gallon trash cans in my garage, one for saltwater and the other connected my RO unit and a float switch. This system makes mixing saltwater and performing water changes a breeze. Plus, I have plenty of water on stand by in case there is an emergency in any of my tanks.